No abstract

A joint research and development program is underway to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. For the MeV range the investigations were focused on charge-state enhancement for ions generated by the modified Bernas ion sources. Based on the previously successful ITEP experience with the e-metal vapor vacuum arc ion source [e.g., Batalin et al., Rev. Sci. Instrum. 75, 1900 (2004)], the injection of a high-energy electron beam into the Bernas ion source discharge region is expected to enhance the production of high charge states. Presented here are construction details and studies of electron-beam influence on the enhancement of ion-beam charge states generated by the modified Bernas ion source.

For the past four years a joint research and development effort designed to develop steady state, intense ion sources has been in progress with the ultimate goal to develop ion sources and techniques that meet the two energy extreme range needs of meV and hundreads of eV ion implanters. This endeavor has already resulted in record steady state output currents of high charge state of antimony and phosphorus ions: P(2+) [8.6 pmA (particle milliampere)], P(3+) (1.9 pmA), and P(4+) (0.12 pmA) and 16.2, 7.6, 3.3, and 2.2 pmA of Sb(3+)Sb(4+), Sb(5+), and Sb(6+) respectively. For low energy ion implantation, our efforts involve molecular ions and a novel plasmaless/gasless deceleration method. To date, 1 emA (electrical milliampere) of positive decaborane ions was extracted at 10 keV and smaller currents of negative decaborane ions were also extracted. Additionally, boron current fraction of over 70% was extracted from a Bernas-Calutron ion source, which represents a factor of 3.5 improvement over currently employed ion sources.

A version of vacuum arc ion source has been developed and constructed at the Institute for Theoretical and Experimental Physics, Moscow, for use with a heavy ion radio frequency quadrupole linac. The source is operated in a pulsed mode with a pulse length from 5 to 120 μs and a repetition rate of from 1/8 to 1 pps. The injection voltage is up to 90 kV depending on the kind of ions being used, and the beam current at the injector output is up to 500 mA. The results described in this article were made at a beam current of from 10 to 100 mA. In order to obtain ions having a charge-to-mass ratio of about 1/60, metals such as Cu, Mo, Ta, W, and Pb were used as the cathode material. Volt-ampere characteristics and charge state distributions were measured. The charge state spectral variation was investigated throughout the arc current pulse duration as well as the dependence of the mean charge state of the beam ions on the melting point of the cathode material.

We report detailed investigations of the electron-beam metal vapor vacuum arc (E-MEVVA) ion source. The experiments were performed in Moscow and Tomsk with nearly the same design of ion sources. We recently reported the first conclusive demonstration of electron-beam enhancement of MEVVA performance using lead and bismuth cathodes, which yielded maximum ion charge states of Pb7+ and Bi8+ for E-MEVVA, as compared to Pb2+ and Bi2+ for conventional MEVVA operation. In this article we report extensive results for additional cathode materials, further details of the Moscow and Tomsk ion sources, and a discussion of electron beam effects on E-MEVVA performance. These results can be considered as a proof of the E-MEVVA principle.